STP73: Definition of pH and Extension of the Acidity Scale to Nonaqueous Systems

    McKinney, D. S.
    Associate Professors of Chemistry and Professor of Chemistry, Carnegie Institute of Technology, Pittsburgh, Pa.

    Fugassi, Paul
    Associate Professors of Chemistry and Professor of Chemistry, Carnegie Institute of Technology, Pittsburgh, Pa.

    Warner, J. C.
    Associate Professors of Chemistry and Professor of Chemistry, Carnegie Institute of Technology, Pittsburgh, Pa.

    Pages: 12    Published: Jan 1947


    Abstract

    This paper is not concerned with the practical difficulties in making pH measurements, such as corrections for liquid junction potentials or the errors inherent in certain electrode systems, since these matters are to be considered in other papers on this symposium. The principal purpose of this paper is the consideration of a number of theoretical difficulties in the definition of the term which place a practical limit on the precision of the pH measurements or on the precision of calculations made from the measurement. The latter part of the paper will consider the even greater difficulty of correlating acidity measurements in nonaqueous solvents with those in water. The majority of industrial processes in which pH measurements are important permit a rather wide tolerance in the pH for successful operation. In these cases, a precision of ±0.3 pH units is usually ample. Since the magnitude of the corrections applied to observations in order to obtain precise pH values seldom exceed 0.3 pH units, it is obvious that for control work the operator need not concern himself with the “fine points” of pH measurement. On the other hand, he should know enough about the process and measuring apparatus to avoid a positive misapplication of the latter and should have a fair knowledge of the inherent errors in order to avoid placing a false significance on the measurements obtained.


    Paper ID: STP47875S

    Committee/Subcommittee: E01.02

    DOI: 10.1520/STP47875S


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